Analyzing a particular component in blood is an effective way to check the condition of a human body or cure a particular disease. For such analysis, use may be made of an analyzer to which a cartridge formed with a fine channel is mounted. To count blood cells such as red blood cells or white blood cells in the blood sample flowing through the fine channel, it is necessary to accurately measure the flow of the blood sample in the cartridge. To grasp the flow accurately, it may be considered to provide the analyzer with e.g. a constant-flow pump as a means to move the blood sample. However, since the cartridge is formed with a fine channel, variation in pressure drop resistance in the flow direction is large. Thus, it is difficult to achieve the constant flow only by a pump. Thus, it is preferable to provide a means for measuring the flow of the blood sample through the fine channel of the cartridge.
FIG. 15 shows a conventional fine channel flowmeter. The flowmeter X shown in the figure measures the flow of the fluid 93 through a channel 92 formed in a substrate 91. Specifically, the flowmeter X measures the flow of the fluid 93 by using an excitation laser beam 94a irradiated through a lens 94 and a detection laser beam 95a irradiated through a lens 95. The excitation laser beam 94a may be infrared to heat the fluid 93 flowing through the channel 92. The detection laser beam 95a may be visible light having a wavelength of e.g. 532 nm. The detection laser beam 95a passed through the fluid 93 is received by a light-receiving apparatus 98 via an infrared filter 96 and a pinhole plate 97. Signals from the light-receiving apparatus 98 are processed by a controller 99. By this process, the index of refraction of the fluid 93 at the portion irradiated with the detection laser beam 95a is computed immediately. The index of refraction of the fluid 93 changes when the fluid is irradiated with the excitation laser beam 94a. The period of time from when the irradiation of the excitation laser beam 94a is started till when a change in index of refraction of the fluid 93 is detected is measured. Based on the period of time and the distance between the irradiation position of the excitation laser beam 94a and that of the detection laser beam 95a, the flow velocity of the fluid 93 through the channel 92 is obtained. By multiplying the flow velocity by the cross sectional area of the channel 92, the flow of the fluid 93 is obtained.
However, to meet the strong demand for size reduction of the cartridge to which the flowmeter X is to be mounted, the cross section of the channel 92 is made small. The smaller the cross section of the channel 92 is, the more necessary it is to converge the excitation laser beam 94a and the detection laser beam 95a into a small spot light and to enhance the accuracy of the irradiation position. That is, the light sources (not shown) of the excitation laser beam 94a and the detection laser beam 95a need to be reduced in size, which makes the manufacture of the analyzer cartridge difficult. In this way, the size reduction of the analyzer cartridge is hindered.
Patent Document 1: JP-A-2005-140756